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Bio-inspired cofacial Fe porphyrin dimers for efficient electrocatalytic CO2 to CO conversion: Overpotential tuning by substituents at the porphyrin rings.

Zahran ZN, Mohamed EA, Naruta Y - Sci Rep (2016)

Bottom Line: Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2.The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO.By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups.

View Article: PubMed Central - PubMed

Affiliation: Institute for Science and Technology Research, Centre for Chemical Energy Conversion, Chubu University, Kasugai 487-8501, Japan.

ABSTRACT
Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO. The location of Ni and Fe at proper positions allows their cooperation for CO2 to CO conversion through a push-pull mechanism. Bio-inspired from CODHs, we used several cofacial porphyrin dimers with different substituents as suitable ligands for holding two Fe ions with suitable Fe-Fe separation distance to efficiently and selectively promote CO2 to CO conversion with high turnover frequencies, TOFs. The substituents on the porphyrin rings greatly affect the catalysis process. By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups. The Fe porphyrin dimers among reported catalysts are the most efficient ones for CO2 to CO conversion. Control experiments indicate that the high performance of the current CO2 to CO conversion catalysts is due to the presence of binuclear Fe centers at suitable Fe-Fe separation distance.

No MeSH data available.


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Catalytic CV responses (left, forward scan only shown for clarity) of three Fe porphyrin dimers (0.5 mM) at 100 mV/s scan rate in DMF/10% H2O saturated with CO2 and the corresponding foot-of-the-wave analysis (right).
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f3: Catalytic CV responses (left, forward scan only shown for clarity) of three Fe porphyrin dimers (0.5 mM) at 100 mV/s scan rate in DMF/10% H2O saturated with CO2 and the corresponding foot-of-the-wave analysis (right).

Mentions: For fast catalytic process, the foot-of-the-wave analysis of the CVs has been reported to be a quick estimation of the catalysis rate constant, kcat, TON, and TOF of the catalysis reaction without the contribution of side phenomena such as substrate consumption, catalyst deactivation, and/or product inhibition1923. The analysis is based on the linear correlation between i/i0p and 1/{1 + exp[F/RT(E − E0cat)]} “equation (7)”,where i is the catalytic current in the presence of CO2, i0p is the peak current in the absence of CO2, F, R, T, and E are the Faraday constant, gas constant, absolute temperature, and the electrode potential, respectively. Plotting i/i0pvs. 1/{1 + exp[F/RT(E − E0cat)]} gives rise to a straight line of slope 2.24(RT/Fν)1/2(kcat)1/2 (ν is the scan rate in V/s) from which the catalysis rate constant, kcat is calculated. The kcatis then used to calculate the TOF and the logTOF −η relationship according to equations (8) and (9), respectively, where TOF0 is the intrinsic turnover frequency (turnover frequency at zero η). The value of η is calculated according to equation (10) based on the reported thermodynamic redox potential of the CO2 to CO conversion in DMF/5% H2O solution containing 0.1 M nBut4NPF6 supporting electrolyte, E0(CO2/CO) = −0.69 V19. Figure 3 depicts the catalytic CVs responses (left) of three Fe porphyrin dimers (0.5 mM, 100 mV/s scan rate) and the corresponding foot-of-the-wave analysis (right). Other catalysts show similar behaviors. Figure 4 shows the catalytic CVs responses (a) of the six Fe porphyrin dimers and the corresponding logTOF −η relationship (b). Table 1 summarizes the catalysis parameters of the current Fe porphyrin dimers and that of the most efficient reported CO2/CO reduction molecular catalysts. The table clearly shows that η for the CO2 reduction decrease by increasing the electron-withdrawing substituents on the porphyrin rings for the Fe porphyrin dimers and their benchmarking superiority for the CO2 to CO conversion activity over the reported catalysts.


Bio-inspired cofacial Fe porphyrin dimers for efficient electrocatalytic CO2 to CO conversion: Overpotential tuning by substituents at the porphyrin rings.

Zahran ZN, Mohamed EA, Naruta Y - Sci Rep (2016)

Catalytic CV responses (left, forward scan only shown for clarity) of three Fe porphyrin dimers (0.5 mM) at 100 mV/s scan rate in DMF/10% H2O saturated with CO2 and the corresponding foot-of-the-wave analysis (right).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834491&req=5

f3: Catalytic CV responses (left, forward scan only shown for clarity) of three Fe porphyrin dimers (0.5 mM) at 100 mV/s scan rate in DMF/10% H2O saturated with CO2 and the corresponding foot-of-the-wave analysis (right).
Mentions: For fast catalytic process, the foot-of-the-wave analysis of the CVs has been reported to be a quick estimation of the catalysis rate constant, kcat, TON, and TOF of the catalysis reaction without the contribution of side phenomena such as substrate consumption, catalyst deactivation, and/or product inhibition1923. The analysis is based on the linear correlation between i/i0p and 1/{1 + exp[F/RT(E − E0cat)]} “equation (7)”,where i is the catalytic current in the presence of CO2, i0p is the peak current in the absence of CO2, F, R, T, and E are the Faraday constant, gas constant, absolute temperature, and the electrode potential, respectively. Plotting i/i0pvs. 1/{1 + exp[F/RT(E − E0cat)]} gives rise to a straight line of slope 2.24(RT/Fν)1/2(kcat)1/2 (ν is the scan rate in V/s) from which the catalysis rate constant, kcat is calculated. The kcatis then used to calculate the TOF and the logTOF −η relationship according to equations (8) and (9), respectively, where TOF0 is the intrinsic turnover frequency (turnover frequency at zero η). The value of η is calculated according to equation (10) based on the reported thermodynamic redox potential of the CO2 to CO conversion in DMF/5% H2O solution containing 0.1 M nBut4NPF6 supporting electrolyte, E0(CO2/CO) = −0.69 V19. Figure 3 depicts the catalytic CVs responses (left) of three Fe porphyrin dimers (0.5 mM, 100 mV/s scan rate) and the corresponding foot-of-the-wave analysis (right). Other catalysts show similar behaviors. Figure 4 shows the catalytic CVs responses (a) of the six Fe porphyrin dimers and the corresponding logTOF −η relationship (b). Table 1 summarizes the catalysis parameters of the current Fe porphyrin dimers and that of the most efficient reported CO2/CO reduction molecular catalysts. The table clearly shows that η for the CO2 reduction decrease by increasing the electron-withdrawing substituents on the porphyrin rings for the Fe porphyrin dimers and their benchmarking superiority for the CO2 to CO conversion activity over the reported catalysts.

Bottom Line: Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2.The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO.By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups.

View Article: PubMed Central - PubMed

Affiliation: Institute for Science and Technology Research, Centre for Chemical Energy Conversion, Chubu University, Kasugai 487-8501, Japan.

ABSTRACT
Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO. The location of Ni and Fe at proper positions allows their cooperation for CO2 to CO conversion through a push-pull mechanism. Bio-inspired from CODHs, we used several cofacial porphyrin dimers with different substituents as suitable ligands for holding two Fe ions with suitable Fe-Fe separation distance to efficiently and selectively promote CO2 to CO conversion with high turnover frequencies, TOFs. The substituents on the porphyrin rings greatly affect the catalysis process. By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups. The Fe porphyrin dimers among reported catalysts are the most efficient ones for CO2 to CO conversion. Control experiments indicate that the high performance of the current CO2 to CO conversion catalysts is due to the presence of binuclear Fe centers at suitable Fe-Fe separation distance.

No MeSH data available.


Related in: MedlinePlus